FRESNO, Calif. — The nine victims in this city's worst mass murder were all killed by gunshots, the police said on Monday.

They said investigators were trying to determine whether the killer, suspected to be the father of all the victims, was helped by someone else.

The bodies — six females and three males ages 1 to 24 — were found on Friday when the police responded to a child-custody call at a house. After a standoff with the suspect, Marcus D. Wesson, 57, they took him into custody. Wesson's arraignment on nine counts of murder has been scheduled for Wednesday.

Three of the victims were a year old, and four others were younger than 9. The other two victims were a 17-year-old girl and a 24-year-old woman, the police said. Two of the toddlers may be the result of incestuous relations between Wesson and his older daughters, the authorities said.

Autopsies on seven of the victims indicate that they suffered gunshot wounds, while injuries on the last two bodies still under examination exhibited injuries similar to gunshot wounds, the authorities said.

The Fresno County coroner's office said one of the victims might have been somehow involved in the shootings. Chief Jerry Dyer of the Fresno Police Department declined to comment about a second killer but said it was "something we are keeping an open mind to."

The police continue to look for next of kin to help with identification of the bodies, and the authorities set up a message center on Monday to cast a wider net. Dyer said more search warrants had been issued for another Fresno address.

The authorities are still trying to assemble a clear picture of what happened at Wesson's house on Friday.

When police officers arrived, two women said they had been trying to pick up their children from the house. At first, Wesson was cooperative and said he would release the children, but then reneged, the police said. The women told the police that Wesson had a firearm, so they called in negotiators and a SWAT team.

After he surrendered, the police discovered the nine bodies, some piled on top of one another, in a small, cluttered room.

The police investigation and interviews with residents provide a portrait of Wesson as an intelligent but extremely controlling and private unemployed man, who may have been supported by the women who gave birth to his children.